Electronic control circuit



June 3, 1952 w, BROWN 2,599,228

ELECTRONIC CONTROL CIRCUIT Filed Dec. 6, 1950 UTILIZATION CIRCUH' Inventor: Robert W- Brown,

His AtCOTYIEV Patented June 3, 1952 UNITED, STATES} PATENT OFFW'E' Robert vW.-Brown, North Syracuse, N. Y,, assignon. to. General Electric. Company; a corporationiofl New, York Application December 6, 1950 S erial l\lo ..1i) 9,5 07 I This inventionrelates to electronic control oincuits"and'particularly' to the type providingfpr ov tection of electrical circuits against possibleoverload.

Prior art devices for protecting electrical circuits against overload have been relatively complex in construction and expensive. In accordance with the invention, these difficultiesare resolved through the use ofa simple electronic circuit controlling a single on-oif relay. This arrangement results in a verysensitive overload protective device which is sufficiently rugged to insure satisfactoryoperation despite shock and vibration. In addition the electronic circuit can be readily adjuSted toaccommOdate high as well as low current consuming loads while maintain-j ing its high sensitivity of operation.

Accordingly, it is an object of my invention to provide an improved electronic control circuit.-

Another object of my invention is to provide a sensitive control circuit which willlock out an overloadedlcircuit.

Another. objectv of my invention is'to provide. a highly sensitiveoverload protection apparatus.

Another. object of my invention is to provide an improved overload protective apparatus for accommodatingv both low and high current consuming. load circuits.

Anotherobjectofmy invention is to provide a control circuit which. is highly sensitive to changes. in electrical signals of J both-high and low intensity.

The novel features .which I believe to be characteristic of my. invention are set forth with particularity in the appendedclaims. My invention itself, however, both as toits organization and method of operation together with further objects and advantages thereof may best be understood by referenceto the following description taken in connection with theiaccompanying drawingillustrating in circuit diagram form an embodiment of my invention.

Referring to. the drawing there. is shown a.

utilization circuitl connectedto the output ofqa full- -waye .rectifier..2. Rectifier} in turnisconlnected to a power. Supply, conventionally. repre! sented as a 110 volts, 60, cyclesource, bymeans of a ground connection and the leadv 3. In:.1ead.=3 there is serially inserted a pair ofvnormally open contactors 4 and 5. The purpose of the associated control circuitry to be described shortly, is to affect closure of contacts 4 and 5 thereby,

permittingenergization of the utilization circuit 1 from the alternating potential source andin' he;.tYtt ii-fi lriijfitt itiwlesd peratin c nd 2 Claims (Cl. 175.-2 9.4)

tions are not encountered at anytimethereafter to open the contacts 4 and 5 thereby de-energiz-i,

conditionslmight bel excessively. high' voltage,- excessive currentfrequency.deviations.or any, com.-

binations of these and similar factors.

Referring to theembodiment illustrated in the drawingthereis shown a relay. winding 6 associatedwith. the contactors 4.and..5. In ordento. control energizationof the winding. a gaseous dischargedevice 1 isprovided. Device .llcomprises.

an anode 8, a.cathode.9,- a screen grid illranda The. gaseous discharge. path. of.-. device 1 isenergizedfromthe llO volt source; through winding 6 connected. betweentheanode... 8 and .oneterminal of the alternating,potential.

control grid 1 l.

source, and through resistor l2 connecting the. cathode 9.via theground connection to. theother terminal of the alternating. potential source.

Between the cathode. 9, and. resistor, I2, there is inserted a normally closed stop switch l3. Re,- sistor l4 and condenser l 5. provide a, ground re.-

turnforthe control gridrl l. A momentarystart. switch It is provided to connect the control.

electrode to the cathodetthrough the nor.- mallyclosed switch l3. A pair of contactors.

and [3; provide, a loekrin. circuit around the.

momentary start switch It. Resistor 19. con-. nectedbetweenlead 3 a junction. 20. provides, a control bias. .forthe,cathode 9..by. dividingsthe. volts. between. resistor l9.. and resistor 12; Operating potential for the, screen grid; I a is ob.v

tained. by connection 21; to. the...center.. tap of secondary. transformers winding. 22 and: series.

connected resistors'23 and I2 connectedb-etvizeenf the screen grid Ii) andground The ,rectifiencircuit .2 is conventional andcomprisesa primaryv transformer winding.v 24: for energizing the. secondary. center tapped. winding 22; terminals of the secondary windingllarecone nected to respective ano des 25. of. a. dualdiode. The. resulting unidirectional i i potential developqiat -.the cathode. 21 islfii'tered' The end 1 3 in the circuit 28 before application to the utilization circuit I.

The switch and contactor positions shown in the drawing correspond to the condition when the load circuit I is unenergized.

It should be noted that the circuit arrangement disclosed provides energization of the gaseous discharge path of device I through the load resistor I2 and the relay winding 6. The use of a gaseous discharge device in the manner disclosed provides a desired switchin action in that the resistance between cathode and anode is high enough to be considered an open circuit as long as the control electrode II is negative with respect to the cathode. However, if the voltage at the control electrode II is made positive enough to ionize thegas in the device I, the resistance between cathode and anode becomes so low as to be negligible in many circuits and will stay that way regardless of what potential is ap plied to the control electrode. This is the condition of conduction of a thyratron and it continues to conduct a relatively high current until the anode and control electrode are brought to within a few volts of each other. The point at which the gaseous discharge device I conducts originally can be varied to a certain degree by the amount of negative potential placed on the shield grid I0. With the control electrode II and cathode 9 tied together, as is contemplated in the arrangement of the drawing, and the shield grid II) maintained at a fixed potential, device 1 conducts whenever a sumciently high positive voltage is supplied to the anode 8 and continues to fire until the anode potential is lowered to within a few volts of the control grid I I. Once the device I conducts it cannot be extinguished in any other way.

If for some reason the shield grid I 6 is supplied with a given negative voltage with respect to the cathode, the potential at the anode 8 must be higher than previously mentioned in order that the device I may conduct. When the rectifier 2 is energized, all of the current drawn by the utilization circuit passes through resistors 23 and I2 to ground thereby developing a negativ potential between the shield grid II and the cathode 9. By varying the value of resistor 23, any desired potential difference may be established between the shield grid and the cathode. Actually, the gaseous discharge device 1 requires only a very small change in the current drawn by the utilization circuit I to provide the small voltage difierences required between the shield grid and the cathode to provide the protective action desired.

The alternating potential bias applied by the voltage divider action of resistors I9 and I2 to the cathode 9, insures that the gaseous discharge device I will not conduct unless the grid II is connected to it. For a given applied cathode to anode potential, a given negative potential applied between cathode 9 and shield grid It will keep the device I from conducting during any portion of the positive going cycle of the alternating potential applied to the anode 8. To energize the utilization circuit, the start switch I6 is momentarily closed and since no negative potential is applied between cathode 9 and the shield grid I due to the normally open contacts 4 and 5, device I conducts on the next positive going cycle of alternating potential applied to anode 8. The resulting electron discharge current flow through the winding 6 causes contactors 4 and to close thereby applying alternating potential over lead 3 to the rectifier circuit 2. Circuit 2 in turn energizes the utilization circuit I. Assuming normal operation of the utilization circuit, the resultant load current flow through the resistors 23 and I2 develops a potential difierence between the shield grid I0 and the cathode 9 of a magnitude slightly greater than that required to prevent subsequent conduction of the device I. In addition, due to current flow in winding 6, contactors I1 and I8 are closed thereby short-circuiting the momentary start switch I6. This connects the control grid II to the cathode 9, thereby permitting continued conduction of the gaseous discharge device. To insure that the winding 6 remains energized during the negative going portions of the alternatin potential applied to the anode 8, condenser 29 is connected across the winding. Thus the energy stored in the condenser 29 during the positive going portions of the applied anode potential discharges through the winding 6 during the negative going portions to maintain current flow therein and insure that contactors 4, 5 and I1, I8 are maintained closed.

In the event the utilization circuit overloads the rectifier 2, the resultant increase in current flow through resistor 23 correspondingly increases the negative potential between the shield grid I0 and the cathode 9. The windin 6 remains energized for the balance of the positive cycle of anode potential, but device I will not conduct on the succeeding positive cycle due to the increased potential between the screen grid and cathode. The contactors 4, 5 and I1, I8 open when the discharge current from the condenser 29 drops below a given level. This immediately de-energizes the utilization circuit I and opens the grid to cathode circuit of tube 1. In order to re-energize the load circuit, the start button I6 must be pressed again to initiate the previously mentioned series of operations. If at any time it is desired to de-energize the load circuit, the stop button may be momentarily opened thereby interrupting gaseous discharge current flow through the winding 6 and permitting the contactors I, 5 and I7, I8 to open.

The sensitivity of the control circuit of the present invention may be best appreciated by considering a practical embodiment in which 115 volts alternating potential was applied to the anode 8 as shown in the drawing. An alternating potential bias of 3.4 volts was developed across resistors I9 and I2 at the cathode 9. This set of voltage conditions required 1.05 volts of negative potential difierence between the shield grid II) and the cathode 9 to keep the thyratron from conducting. In this particular instance, the utilization circuit I consumed milliamperes of current from the rectifier circuit 2. Accordingly, a resistor of 100 ohms was employed for 23, developing a negative 1 volt of potential across it. As long as the current consumed by the utilization circuit stayed below milliamperes, the utilization circuit I was main tained energized. However, as soon as the current drawn by circuit I thru resistor 23 reached 105 milliamps, the device I was prevented from conducting, thereby disconnecting the utilization circuit I from the power supply.

The simple manner in which the bias for the screen grid It is obtained permits ready application of the circuit to accommodate high as well as low current consuming circuits while maintaining a high degree of sensitivity.

While a specific embodiment has been shown and described, it will be understood that various modifications may be made and developed departing from the invention. The appended claims are, therefore, intended to cover any such modifications within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An overload protective apparatus for a load circuit comprising a two terminal source of alter 1 nating potential, a gaseous discharge device including an anode, a cathode, a control grid and a shield grid, a relay including an operating winding and a pair of normally open contacts for con necting said circuit to said source, said winding connecting said anode to one terminal of said source, said load circuit including a first and a second resistance connected in series between said shield grid and said other terminal, a third resistance connected between the junction of said first, and second resistances and said one terminal, means connecting said cathode to the junction of said resistances, means connecting said control electrode to said other terminal, a normally open switch connected between said control grid and cathode, the alternating potential bias developed across said second resistor between said cathode and said other terminal nor mally maintaining said device non-conductive during positive excursions of the alternating po-= tential applied between said anode and said cathode, and another pair of normally open contacts included in said relay and paralleled with said switch to maintain conduction in said device during positive excursions of the alternating potential applied between said anode and said cathode, said device being responsive to a change in shield grid-to-cathode potential resulting from current flow in said resistances above a given amplitude for rendering said device 40 non-conductive.

2. A control system for selectively conditioning an energizing circuit for a utilization device comprising a gaseous discharge device including an anode, a cathode and a pair of control electrodes, a source of alternating potential having one terminal coupled to said anode and another terminal coupled to one of said control electrodes, a voltage-dividing impedance including end portions connected to said terminals of said source and a portion intermediate said end portions connected to said cathode for providing a bias potential between said cathode and said one control electrode of a magnitude sufficient to prevent conduction in said device, another impedance included in series relation with said energizing circuit and coupled to said cathode and to the remaining one of said control elec trodes to provide another bias potential for controlling conduction in saiddevice in response to the amount of current flow in said energizing circuit, a relay device having a pair of electrical contacts in series relation with said energizing circuit and a contact-actuating winding included in the anode-cathode current path of said device responsive to a change in current flow in said path for actuating said contacts, and means for reducing said first-mentioned bias Potential to initiate conduction in said device.

ROBERT W. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

